Has the risk of dislocation after total hip arthroplasty performed for displaced femoral neck fracture improved with modern implants?

Background: Displaced femoral neck fractures (DFNF) in the elderly can be treated with hemiarthroplasty or total hip arthroplasty (THA). One concern with utilizing THA in this setting is post-operative dislocation. The purposes of this study were to determine the incidence of hip dislocation following THA for DFNF and to identify risk factors for dislocation.

Methods: The charts of 66 posterior-approach THA cases performed for DFNF with mean post-operative follow-up of 4.4 years were retrospectively reviewed. Pre-operative patient demographic data and intra-operative clinical data were recorded including age, race, gender, height, weight, body mass index (BMI), femoral head diameter, acetabular cup diameter, use of an elevated liner, and cementing of femoral component. For patients with available post-operative pelvis radiographs, acetabular cup inclination and version angles were also calculated.

Results: Four dislocation (4/66, 6%) events occurred at an average of 51 days after surgery. No specific risk factors for dislocation were identified but the use of a cemented femoral stem did approach significance (p = 0.06). 47% of the acetabular cups were located outside of the Lewinnek safe zone. Although the dislocation rate of THAs with acetabular cups outside of the safe zone was higher than the dislocation rate for THAs with cups in the safe zone (12.5% vs 0%), placement of acetabular cups outside of the safe zone was not a risk factor for dislocation.

Conclusions: Posterior THA with proper cup positioning and meticulous soft tissue repair is an effective treatment option for DFNF with low dislocation risk.